It is often the case where a packing box which stores products therein is arranged in a stacked state during transportation or after the packing box is transported to a sales shop. U.S. Pat. No. 4,871,067 discloses a packing box where a reinforcing panel extending from a bottom panel to a ceiling panel is provided to corner portions of an outer peripheral panel, and such a packing box has high strength against pressure suitable for stacking. The packing box includes: a bottom panel; end panels connected to both ends of the bottom panel; and side panels connected to both sides of the bottom panel. Edge panels adhered to inner side surfaces of the side panel are connected to both sides of end panels, and the reinforcing panels are connected to the edge panels. Inner panels adhered to inner side surfaces of the end panels are connected to the reinforcing panels.
In the case of this packing box, at the time of assembling the packing box, it is necessary to adhere two or more kinds of panels to each other using an adhesive agent (hotmelt) made of a hot-melt resin, an adhesive agent made of a vinyl acetate emulsion or the like and hence, assembling operability is poor. To be more specific, the end panels and the side panels are folded against the bottom panel, and the edge panels are folded against the end panels and are arranged on the inner side surfaces of the side panels. The reinforcing panels and the inner panels are folded against the edge panels, and the inner panels are arranged on the inner side surfaces of the end panels. It is necessary to adhere the side panels to the edge panels and to adhere the inner panels to the end panels while maintaining such a folded state. Accordingly, the assembling operability is poor.
In view of the above, there has been a demand for the improvement of assembling operability while maintaining high strength against pressure from product manufacturers of products. A case is considered where a cumbersome assembling operation is performed by a box manufacturer, and packing boxes in an assembled state are supplied to a product manufacturer. In this case, however, the number of packing boxes which can be transported to the product manufacturer from the box manufacturer becomes small. Further, it is necessary for the product manufacturer to ensure a large storage space for storing unused packing boxes and hence, a cost is pushed up.